1. Field of the Invention
The present invention relates to testing techniques for elements within integrated circuits, and in particular, to testing techniques for measuring characteristics of ferromagnetic materials in integrated circuits.
2. Related Art
As the dimensions of circuit devices (e.g., transistors) continue to decrease, the size of the average die needed for a given integrated circuit (IC) has also decreased. Additionally, circuit densities have increased. Accordingly, for a given die size, the number of circuits and subsystems have increased, thereby allowing the level of integration to increase. In the case of radio frequency (RF) circuits and systems, this has meant that more and larger portions of the subsystems have been integrated into a single IC. Further, as the frequencies of operation increase, it becomes increasingly important to also integrate more of the necessary reactive components (e.g., capacitors and inductors) within the IC. While capacitors can be implemented using various semiconductor structures, including transistor structures, implementing inductors requires the use of ferromagnetic materials.
However, a number of difficulties are encountered when trying to perform the measurements necessary for characterizing ferromagnetic materials implemented in an IC environment, particularly in a production environment and for high signal frequencies. A common instrument used for characterizing ferromagnetic materials has been a vibrating sample magnetometer (VSM), which is used to measure B-H curves to determine permeability. However, using a VSM in a production environment is a non-trivial task, since the material to be characterized must be placed, e.g., suspended, within a uniform magnetic field and forced to undergo mechanical vibration, e.g., induced directly or indirectly (e.g., via control of a piezoelectric structure). Moreover, operation of a VSM is typically limited to very low frequencies, e.g., less than 100 Hertz.
Accordingly, it would be desirable to have a method for measuring permeability of a ferromagnetic material for use in an integrated circuit operating at high signal frequencies, particularly within a production environment.